Installation systems for installing hardware (such as fasteners) to metal panels, are well known in the art. For example, U.S. Pat. No. 4,765,057 discloses a self-attaching fastener, panel assembly, and installation apparatus. Also, U.S. Pat. No. 4,505,416 discloses a fastener installation apparatus for installing fasteners, particularly pierce or clinch nuts, in a reliable, simplified fashion.
Although the above-referenced patents disclose systems for installing fasteners, they all rely on the assumption that once the fastener installation apparatus is properly "set up" for a given style of fastener, a given panel metal thickness, and other related parameters, all future applications having such parameters will result in acceptable installations. Although this assumption is accurate in many applications, there are instances where it is highly desirable to automatically adjust certain features of the installation apparatus to ensure the highest quality installation.
One problem frequently encountered in fastener installations is variations in the panel thickness. Normally, the installation apparatus, which has an installation head mounted to one of the platens of a press, is pre-adjusted for a certain specified thickness of metal, such as steel. However, the thickness of the material is not constant and, in fact, can vary widely, even though within acceptable tolerances. For example, hot rolled steel sheets having a width of 300 mm to 510 mm have a thickness tolerance of plus 0.25 mm for a thickness of 1.43 mm to 1.14 mm. As should be appreciated, this amount of variation can affect the performance of the installed fastener. In this example, the surface of the steel sheet which is engaged by the fastener head can vary from between 0 to 0.25 mm. In this range, the installation head will hit the material with varying force from light to heavy depending upon the panel thickness, which is varying between 0 and 0.25 mm. A force between light and heavy is the ideal installation force with the light and heavy hits being undesirable.
Another problem encountered in fastener installations is machine or press drift from a set shut height. This drift of the press from a preset shut height can be due to many factors, but is commonly due to press wear. There is little or no control over press drift, with the consequences being improperly installed fasteners.
A still further problem can occur in larger presses wherein it is difficult to control the parallelism of the platen with respect to the bolster. With more than one installation head, if the platen stroke is not parallel with respect to the bolster, light and hard hits will result and produce improperly installed fasteners.
Although it is possible to vary the shut height of the press, this is not a feasible solution in applications that are having more than one operation performed in a single stroke, which is the typical situation. The shut height is measured when the press is bottomed out, or shut, and is the distance between the bottom face of the platen and the top face of the base on which the panel to be worked is resting. This shut height is predetermined and can only be varied by changing the location of the rams; i.e., moving them with respect to one another. If the shut height is varied, it will affect all other operations, possibly compounding the adverse effect on the operations being performed on the panel.
What is needed is an apparatus and method that individually adjusts, and in some applications, automatically adjusts the affected nut installation apparatus to account for variations in the thickness of the material. In this way, thickness variations across the width and the length of the material can be monitored and adjustments made to ensure uniform installation of fasteners in a panel.
In addition to the variance in nominal panel thickness, there are other factors which could affect the integrity of the joint made between a fastener and a panel. Some of these factors include a broken or misaligned installation apparatus or fastener, the use of improper material (both fastener and panel), normal wearing of the installation tools, etc.
Thus, in view of the above, it is an object of this invention to provide a system for installing fasteners into a panel wherein the system senses one or more operational parameters and can individually adjust installation apparatus in response to the sensed parameters to ensure a consistent, high integrity joint between the fastener and panel. Another object is to record, restore, and maintain statistical process control data on every panel as opposed to random sampling.